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History
Before the mid-1960s, computers were extremely expensive and used only for special-purpose tasks. A simple batch processing arrangement ran only a single "job" at a time, one after another. But during the 1960s faster and more affordable computers became available. With this extra processing power, computers would sometimes sit idle, without jobs to run.Programming languages in the batch programming era tended to be designed, like the machines on which they ran, for specific purposes (such as scientific formula calculations or business data processing or eventually for text editing). Since even the newer, less expensive machines were still major investments, there was a strong tendency to consider efficiency to be the most important feature of a language. In general, these specialized languages were difficult to use and had widely disparate syntax.
As prices decreased, the possibility of sharing computer access began to move from research labs to commercial use. Newer computer systems supported time-sharing, a system which allows multiple users or processes to use the CPU and memory. In such a system the operating system alternates between running processes, giving each one running time on the CPU before switching to another. The machines had become fast enough that most users could feel they had the machine all to themselves. In theory, timesharing reduced the cost of computing tremendously, as a single machine could be shared among hundreds of users.
[edit] Early years: the mainframe and mini-computer era
The original BASIC language was designed in 1964 by John Kemeny and Thomas Kurtz[3] and implemented by a team of Dartmouth students under their direction. BASIC was designed to allow students to write programs for the Dartmouth Time-Sharing System. It was intended to address the complexity issues of older languages with a new language design specifically for the new class of users that time-sharing systems allowed—that is, a less technical user who did not have the mathematical background of the more traditional users and was not interested in acquiring it. Being able to use a computer to support teaching and research was quite novel at the time. In the following years, as other dialects of BASIC appeared, Kemeny and Kurtz's original BASIC dialect became known as Dartmouth BASIC.The eight design principles of BASIC were:
- Be easy for beginners to use.
- Be a general-purpose programming language.
- Allow advanced features to be added for experts (while keeping the language simple for beginners).
- Be interactive.
- Provide clear and friendly error messages.
- Respond quickly for small programs.
- Not to require an understanding of computer hardware.
- Shield the user from the operating system.
The designers of the language decided to make the compiler available free of charge so that the language would become widespread. They also made it available to high schools in the Hanover area and put a considerable amount of effort into promoting the language. As a result, knowledge of BASIC became relatively widespread (for a computer language) and BASIC was implemented by a number of manufacturers, becoming fairly popular on newer minicomputers like the DEC PDP series and the Data General Nova. The BASIC language was also central to the HP Time-Shared BASIC system in the late 1960s and early 1970s, and the Pick operating system. In these instances the language tended to be implemented as an interpreter, instead of (or in addition to) a compiler.
Several years after its release, highly respected computer professionals, notably Edsger W. Dijkstra, expressed their opinions that the use of GOTO statements, which existed in many languages including BASIC, promoted poor programming practices.[4] Some have also derided BASIC as too slow (most interpreted versions are slower than equivalent compiled versions) or too simple (many versions, especially for small computers, left out important features and capabilities).
Explosive growth: the home computer era
BASIC also had the advantage that it was fairly well-known to the young designers and computer hobbyists who took an interest in microcomputers, and generally worked in the electronics industries of the day. Kemeny and Kurtz's earlier proselytizing paid off in this respect and the few hobbyists' journals of the era were filled with columns that made mentions of the language or focused entirely on one version compared to others.
One of the first to appear for the 8080 machines like the Altair was Tiny BASIC, a simple BASIC implementation originally written by Dr. Li-Chen Wang, and then ported onto the Altair by Dennis Allison at the request of Bob Albrecht (who later founded Dr. Dobb's Journal). The Tiny BASIC design and the full source code were published in 1976 in DDJ.
In 1975, MITS released Altair BASIC, developed by Bill Gates and Paul Allen as the company Micro-Soft, which grew into today's corporate giant, Microsoft. The first Altair version was co-written by Gates, Allen, and Monte Davidoff. Versions of Microsoft BASIC (also known then, and most widely as M BASIC or MBASIC) was soon bundled with the original floppy disk-based CP/M computers, which became widespread in small business environments. As the popularity of BASIC on CP/M spread, newer computer designs also introduced their own version of the language, or had Micro-Soft port its version to their platform.
When three major new computers were introduced in what Byte Magazine would later call the "1977 Trinity",[5] all three had BASIC as their primary programming language and operating environment. Commodore Business Machines paid a one-time fee for an unlimited license to a version of Micro-Soft BASIC that was ported to the MOS 6502 in their PET computer, while Apple II and TRS-80 both introduced new, largely similar versions of the language. The similarities are striking because the first 50 tokens, used for conserving memory, were all the same. As new companies entered the field, additional versions were added that subtly changed the BASIC family. The Atari 8-bit family had their own Atari BASIC that was modified in order to fit on an 8 kB ROM cartridge. The BBC published BBC BASIC, developed for them by Acorn Computers Ltd, incorporating many extra structuring keywords. Most of the home computers of the 1980s had a ROM-resident BASIC interpreter, allowing the machines to boot directly into BASIC. Because of this legacy, there are more dialects of BASIC than there are of any other programming language.
As the popularity of BASIC grew in this period, magazines (such as Creative Computing Magazine in the US) published complete source code in BASIC for games, utilities, and other programs. Given BASIC's straightforward nature, it was a simple matter to type in the code from the magazine and execute the program. Different magazines were published featuring programs for specific computers, though some BASIC programs were considered universal and could be used in machines running any variant of BASIC (sometimes with minor adaptations). Correcting the publishing errors that frequently occurred in magazine listings was an educational exercise in itself.
BASIC source code was also published in fully-fledged books: the seminal examples being David Ahl's BASIC Computer Games series.[6][7][8] Later packages, such as Learn to Program BASIC would also have gaming as an introductory focus.
The ubiquity of BASIC interpreters on personal computers was such that textbooks once included simple "Try It In BASIC" exercises that encouraged students to experiment with mathematical and computational concepts on classroom or home computers. Futurist and sci-fi writer David Brin mourned the loss of ubiquitous BASIC in a 2006 Salon article.[11]
Examples
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Unstructured BASIC
New BASIC programmers on a home computer might start with a simple program similar to the Hello world program made famous by Kernighan and Ritchie. This generally involves simple use of the language's PRINT statement to display the message (such as the programmer's name) to the screen. Often an infinite loop was used to fill the display with the message. Most first generation BASIC languages such as MSX BASIC and GW-BASIC supported simple data types, loop cycles and arrays. The following example is written for GW-BASIC, but will work in most versions of BASIC with minimal changes:10 INPUT "What is your name: ", U$ 20 PRINT "Hello "; U$ 30 INPUT "How many stars do you want: ", N 40 S$ = "" 50 FOR I = 1 TO N 60 S$ = S$ + "*" 70 NEXT I 80 PRINT S$ 90 INPUT "Do you want more stars? ", A$ 100 IF LEN(A$) = 0 THEN GOTO 90 110 A$ = LEFT$(A$, 1) 120 IF A$ = "Y" OR A$ = "y" THEN GOTO 30 130 PRINT "Goodbye "; U$ 140 END
[edit] Structured BASIC
Second generation BASICs (for example QuickBASIC and PowerBASIC) introduced a number of features into the language, primarily related to structured and procedure-oriented programming. Usually, line numbering is omitted from the language and replaced with labels (for GOTO) and procedures to encourage easier and more flexible design.[12]INPUT "What is your name: ", UserName$ PRINT "Hello "; UserName$ DO INPUT "How many stars do you want: ", NumStars Stars$ = STRING$(NumStars, "*") PRINT Stars$ DO INPUT "Do you want more stars? ", Answer$ LOOP UNTIL Answer$ <> "" Answer$ = LEFT$(Answer$, 1) LOOP WHILE UCASE$(Answer$) = "Y" PRINT "Goodbye "; UserName$
[edit] BASIC with object-oriented features
Third generation BASIC dialects such as Visual Basic, REALbasic, StarOffice Basic and BlitzMax introduced features to support object-oriented and event-driven programming paradigm. Most built-in procedures and functions now represented as methods of standard objects rather than operators.The following example is in Visual Basic .NET:
Public Class StarsProgram Public Shared Sub Main() Dim UserName, Answer, stars As String, NumStars As Integer Console.Write("What is your name: ") UserName = Console.ReadLine() Console.WriteLine("Hello {0}", UserName) Do Console.Write("How many stars do you want: ") NumStars = CInt(Console.ReadLine()) stars = New String("*", NumStars) Console.WriteLine(stars) Do Console.Write("Do you want more stars? ") Answer = Console.ReadLine() Loop Until Answer <> "" Answer = Answer.Substring(0, 1) Loop While Answer.ToUpper() = "Y" Console.WriteLine("Goodbye {0}", UserName) End Sub End Class
[edit] Data types and variables
Minimal versions of BASIC had only integer variables and single-letter variable names. More powerful versions of BASIC offered floating-point arithmetic, and variables could be labelled with names six or more characters long.String variables are usually distinguished by having $ suffixed to their name, and string values are typically enclosed in quotation marks.
Arrays in BASIC could contain integers, floating point or string variables.
[edit] List of typical BASIC keywords
[edit] Data manipulation
- LET Command - assigns a value (which may be the result of an expression) to a variable.
- DATA Statement - holds a list of values which are assigned sequentially using the READ Command.
[edit] Program flow control
- IF ... THEN ... ELSE Statement - used to perform comparisons or make decisions.
- FOR ... NEXT Statement - repeat a section of code a given number of times. A variable that acts as a counter is available within the loop.
- WHILE ... WEND and REPEAT ... UNTIL Commands - repeat a section of code while the specified condition is true. The condition may be evaluated before each iteration of the loop, or after.
- GOTO Command - jumps to a numbered or labelled line in the program.
- GOSUB Command - temporarily jumps to a numbered or labelled line, returning to the following line after encountering the RETURN Command. This is used to implement subroutines.
- ON ... GOTO/GOSUB Command - chooses where to jump based on the specified conditions. See Switch statement for other forms.
[edit] Input and output
- PRINT Statement - displays a message on the screen or other output device.
- INPUT Statement - asks the user to enter the value of a variable. The statement may include a prompt message.
- TAB or AT Function - sets the position where the next character will be shown on the screen or printed on paper.
[edit] Miscellaneous
- REM (Remark) - holds a programmer's comment; often used to give a title to the program and to help identify the purpose of a given section of code.
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